Add MemoryInfoStat to Process and fill it while reading /proc/<pid>/status

Main reason: add swap stats per process.
* added MemoryInfoStat to Process as *memInfo
* fill MemoryInfoStat from /proc/<pid>/status , we read it anyway
* it's faster than smaps when quering many processes
* /proc/<pid>/smaps are not always present, it requires CONFIG_PROC_PAGE_MONITOR option to be set